1.  17 O proxy of anthropogenic influences on atmospheric reactivity: Towards model interpretation of the ice core record Becky Alexander, Rokjin J. Park, Daniel J. Jacob Harvard University Justin McCabe and Mark H. Thiemens University of California, San Diego Joël Savarino Laboratoire de Glaciologie et Geophysique de l’Environement American Chemical Society August 25, 2004

2. Source: National Ice Core LaboratoryOverview Oxidation capacity of the atmosphere  17 O sulfate Greenland ice core record (Milcent and Site A) GEOS-CHEM Model – What controls  17 O variability in Arctic? – How well does it agree with measurements? Non-photochemical sulfate production in Arctic

3. Secondary Species HNO 3, HCHO, CO 2, H 2 SO 4, O 3, … Oxidizing Power of the Atmosphere Volcanoes Marine Biogenics Biomass burning Continental Biogenics Primary Species H 2 S, SO 2, CH 4, CO, DMS, CO 2, NO, N 2 O, particulates OH Primary Emissions NO x, Isoprene, SO 2, CH 4, … Industry h  H 2 O

4. Current knowledge of the past oxidative capacity of the atmosphere Measurements Year AD 1870189019101930195019701990 0 10 20 30 40 50 60 O 3 (ppb) H 2 O 2 (  M) Sigg & Neftel, 1991 Summit 0 2 4 6 1750200018501950 18001900 H2O2H2O2 O3O3

5. Source of  17 O Sulfate SO 2 in isotopic equilibrium with H 2 O :  17 O of SO 2 = 0 ‰ 1) SO 3 2- + O 3 (  17 O=35‰)  SO 4 2-  1 7 O = 8.75 ‰  17 O of SO 4 2- a function relative amounts of OH, H 2 O 2, and O 3 oxidation Savarino et al., 2000 3) SO 2 + OH (  17 O=0‰)  SO 4 2-  17 O = 0 ‰ 2) HSO 3 - + H 2 O 2 (  17 O=1.7‰)  SO 4 2-  17 O = 0.85 ‰ Aqueous Gas

6. Greenland, Site A SO 4 2- nss [ppb] NO 3 - [ppb] Alexander et al., 2004 GISP data from Mayewski et al., 1997 and NSIDC

7. Greenland, Site A  17 O Alexander et al., 2004 PIH:  17 O SO 4 2- = 1.0‰ Present:  17 O SO 4 2- = 1.9‰

8. Milcent + Site A  17 O  17 O nssSO 4 2- (‰) Milcent data: Alexander, Savarino and Thiemens, unpublished data  17 O meas = ƒ OH *0‰ + ƒ H2O2 *0.85‰ + ƒ O3 *8.75‰ ƒ OH + ƒ H2O2 + ƒ O3 = 1

9. GEOS-CHEM: Global 3D CTM http://www-as.harvard.edu/chemistry/trop/geos/index.html Bey et al., 2001; Park et al., 2004, Alexander et al., 2004, manuscript in preparation SO 2 H 2 SO 4 OH New particle formation CCN Light scattering DMS OHNO 3 H 2 O 2, O 3 SO 4 2- O3O3 Sea-salt aerosol pH = 4.5

10. 0.0 1.63.24.7 6.3 ‰ JanuaryJuly GEOS-CHEM: Seasonal Variability in  17 O Sulfate 0 2 4 6 8 0 1234  17 O sulfate (‰) H 2 O 2 (ppbv) HSO 3 -, H 2 O 2, O 3

11. Northern Hemisphere Perspective 1.9‰ Site A (1930-1980) 1.9‰ 1.0‰ Alert 1.0‰ McCabe, Savarino and Thiemens, unpublished data Alexander et al., 2004

12. Arctic Measurements Measurements: Justin McCabe, UCSD, personal communication GEOS-CHEM Measurements Alert (82°N, 85°W)

13. Arctic Night-time Chemistry S IV + ½ O 2  S VI Mn 2+, Fe 3+  17 O = 0‰ ?? From Sirois and Barrie, 1999 xV (ng m -3 )xMn (ng m -3 ) Savarino et al., 2001

14. GEOS-CHEM Measurements GEOS-CHEM [Fe(III)] = 0.5  mol/l [Mn(II)] = 0.05  m/l Measurements Alert: Metal Catalysis? GEOS-CHEM [Fe(III)] = 0.5  mol/l [Mn(II)] = 0.05  m/l [Fe(III)] = 5.0  mol/l [Mn(II)] = 0.5  m/l Measurements

15. Conclusions  17 O provides first conservative constraint on anthropogenic impacts on the oxidation capacity of the atmosphere Need a global model to interpret quantitatively GEOS-CHEM  17 O sulfate variability in high Northern latitudes controlled by H 2 O 2 /OH concentrations in present day. Preindustrial? Alert measurements indicate non-photochemical source of sulfate in present day atmosphere

16. Acknowledgements